I've been on Duolingo for about a month now, and they must be getting a bit sick of me because I submit a lot of beta feedback---but they're very responsive and

I've been on Duolingo for about a month now, and they must be getting a bit sick of me because I submit a lot of beta feedback---but they're very responsive and usually pretty good about fixing things, sometimes by the next day, including when I type a translation that was correct but marked wrong by the program. I agree with the OP that it's overall a great site, although there are a few lingering things that they seem unable to fix, mostly minor; for instance, the "practice" is too irritating to keep up with because its randomness is broken and literally every batch of twenty includes at least six to eight occurrences of the sentence "Sie liest die Zeitung" and/or "Der Mann liest die Zeitung". Argh. But the larger, systemic problem with it is that I don't think it works as advertised for raw newbies to the language. It's perfect for those of us who dimly remember the "rules" of a language and just need a lot of structured practice to get up to speed. But by presenting nothing but example text to translate, they're basically asking the newbie to induce a complete grammar of the language without any guidance, and while children learn their first language(s) that way, adults don't. (Example: in German, the ending that attaches to an adjective can be one of six or seven things depending on the case of the phrase, the gender and number of the noun it attaches to, and the definiteness of the article that commands the phrase. None of this is explained within Duolingo; it just throws a bunch of example sentences at you, never talking about gender, number, case, or definiteness (two of which are concepts that aren't even relevant to English grammar). That's... tricky.) On the crowdsourcing translation front, it has an incredible strength, which is that native English speakers will be great at evaluating whether a sentence is fluent, valid English. But it has an incredible weakness, which is that native English speakers who are just learning German are much less good at evaluating whether a sentence is a valid translation of what the German sentence says. I've seen quite a few situations where a particular translation has been heavily upvoted despite missing some crucial part of the source sentence's meaning (and in a few cases, meaning exactly the opposite). But it's a work in progress, of course. It seems to have a lot of promise, so perhaps they can surmount these difficulties.